One of the challenges in generating Three Dimensional (3D) ultrasound images may be the high data acquisition rate needed to scan tissue at a desired rate (such as 22 scans per second (sps)). The data acquisition rate may be a function of the size of the volume scanned, including depth, and the desired frame rate. For example, the data acquisition rate of a 3D ultrasound imaging system that performs 22 sps may need to increase as the size of the volume scanned increases. It is known to increase the data acquisition rate of 3D ultrasound imaging systems by using parallel receive processing. Parallel receive processing for a conventional 3D ultrasound imaging system is discussed in U.S. Pat. No. 4,694,434 entitled "Three-Dimensional Imaging System" to von Ramm and Smith which is incorporated herein by reference.
As shown in FIG. 1, a volume 100 may be scanned by steering ultrasound beams 115 into the volume 100 over an azimuth angle 110 and an elevation angle 120 using a two dimensional (2D) array of ultrasound transducer elements 130. For example, the volume 100 may be scanned by steering 256 ultrasound beams into the volume 100 (16 transmit ultrasound beams through an azimuth angle of 65 degrees combined with 16 transmit ultrasound beams through an elevation angle of 65 degrees). The 256 ultrasound beams may be processed using parallel receive processing to form 4096 ultrasound scan lines (16 ultrasound scan lines formed for each transmit ultrasound beam transmitted). Accordingly, parallel receive processing may be used to increase the data acquisition rate by a factor of 16. However, increasing the data acquisition rate further using parallel receive processing may be prohibitively expensive to implement and may adversely affect the quality of images generated by conventional 3D ultrasound imaging systems.
The ultrasound scan lines may be used to provide a three dimensional (3D) data set that represents the volume 100. Conventionally, the 3D data set may be manipulated by a user to view selected portions of the volume. For example, the user may select slices of the volume for viewing. Accordingly, the 3D data set may be accessed to provide the data which corresponds to the selected slices of the volume 100 which is then displayed.
As described in U.S. Pat. No. 5,546,807 entitled "High Speed Volumetric Ultrasound Imaging System" to Oxaal et al., which is incorporated herein by reference, a volume is scanned to provide a representative 3D data set which is stored in a memory. Subsequently, slices of the volume 100 may be selected by the user. The data which corresponds to the selected slices of the volume 100 is retrieved from the memory and displayed. The selected slices may be B-mode (B) slices, Constant Depth (C) slices, and Inclined (I) slices as shown in FIGS. 2-4 respectively.
FIGS. 2-4 illustrate slices of the volume 100 selected for viewing as described in Oxaal et al. As shown in FIG. 2, the volume 100 is scanned to a range 205 and B slices 200, 210 are selected for viewing, whereupon the data which corresponds to the selected B slices is retrieved from the 3D data set to provide views of the B slices 200, 210. As shown in FIG. 3, a C-slice 300 may also be selected from the 3D data set for viewing. Accordingly, the data which corresponds to the C slice 300 is selected from the 3D data set and displayed. As shown in FIG. 4, first and second I slices 400, 401 are selected from the 3D data set for viewing. In particular, the first I slice 400 is tilted in the volume 100 so that the top of the first I slice 400 is closer to the 2D array of ultrasound transducer elements than the bottom of the first I slice 400. Similarly, the second I slice 401 is tilted in the volume 100 so that the top of the second I slice 401 is closer to the 2D array of ultrasound transducer elements than the bottom of the second I slice 401.
Unfortunately, the time needed to scan the volume 100 in each of the cases shown in FIGS. 2-4 may limit the data acquisition rate of conventional 3D ultrasound imaging systems. For example, a conventional 3D ultrasound imaging system may need to complete a first scan of the volume 100 before starting a second scan. Therefore, the size of the volume 100 may limit the data acquisition rate of the conventional 3D ultrasound imaging system.
It is also known to use two orthogonal linear arrays to produce two orthogonal B slices as described in "Real-Time Orthogonal Mode Scanning of the Heart. I. System Design," J. Amer. Coll. Cardiol., Vol. 7, 1986, pp. 1279-1285 by Snyder et al., which is incorporated herein by reference. Unfortunately, the system discussed by Snyder et al. may not be capable of scanning B slices which are oriented at a non-orthogonal angle with respect to each other and the two dimensional array of ultrasound transducer elements.
As described above, the data acquisition rate of conventional 3D ultrasound imaging systems may need to be increased as the size of the volume scanned is increased or as the desired frame rate is increased. The size of the volume scanned may be increased by increasing the depth of the scan or increasing the angle over which the scan is performed. For example, increasing the data acquisition rate may allow an increase in the azimuth angle from 60.degree. to 80.degree.. Alternatively, increasing the data acquisition rate may be used to provide deeper scans while maintaining a desired fame rate. Accordingly, there is a need to further increase the data acquisition rate of 3D ultrasound imaging systems.